Valved catheters including high flow rate catheters

ABSTRACT

A pressure activated two-way slit valve assembly is designed to be used in combination with, but not limited to, a high flow rate catheter to prevent accidental ingestion of air or loss of blood if the closure cap comes off during non-use of the catheter. In addition, the potential for occlusion of the catheter due to blood clots in the catheter and catheter related infection is substantially reduced. The pressure activated two-way slit valve assembly includes a first end, a second end, a wall defining a dumbbell shaped channel, and a flexible, thin disk having a slit and positioned within the pressure activated two-way slit valve assembly to reside within the dumbbell shaped channel. The slit and the dumbbell shaped channel are sized to enable the slit to deform in response to a predetermined pressure differential across the slit to allow fluid to pass therethrough.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of, and claims priority to, U.S. application Ser. No. 11/765,956, filed on Jun. 20, 2007, now U.S. Pat. No. 8,077,987, which is in turn a continuation of U.S. application Ser. No. 10/651,535, filed on Aug. 29, 2003, now U.S. Pat. No. 7,252,652.

TECHNICAL FIELD

This invention relates to valves for catheters. More particularly, this invention relates to a valved high flow rate catheter

BACKGROUND INFORMATION

A high flow rate catheter is a tubular medical device defining one or more lumens for transporting fluids to and/or from a patient's body at a high flow rate, e.g. greater than 200 ml/min. An example of a commonly used high flow rate catheter is a hemodialysis catheter. Hemodialysis catheters include at least one lumen for transporting a patient's waste-filled blood to a dialysis machine for treatment, and another lumen for carrying the treated blood back to the patient. Generally, hemodialysis catheters are implanted within a patient's body such that a portion remains within a blood vessel of the patient and a portion extends outside of the patient body to be connected to the dialysis machine.

Conventionally, clamps that compress the lumens of the hemodialysis catheter have been used to prevent blood loss and to prevent ingestion of air through the catheter and into a patient's blood stream (i.e., when the catheter is not in use). These clamps tend to degrade the hemodialysis catheter, thereby requiring medical professionals to remove and replace these catheters frequently. In addition, conventional high flow rate catheters are associated with a high occurrence of occlusion formation and infections.

SUMMARY OF THE INVENTION

The present invention generally relates to valves for catheters. While the present invention is described with regard to high flow rate catheters, it should noted that the valves described herein may be used in combination with any type of catheter. Devices according to the invention are typically used to transport fluids to and/or from a patient's body at a high flow rate when the device is in use. It is an object of this invention to provide a device that protects against catastrophic events when the catheter is not in use, such as, for example, ingestion of air through the device into the patient's blood stream or blood flowing uncontrollably out from a patient's body. It is another object of the invention to reduce occlusion formation and infections associated with conventional high flow rate catheters.

In one aspect, the invention relates to a pressure activated two-way slit valve assembly for a catheter. The pressure activated two-way slit valve assembly includes a first end, a second end, a wall defining a dumbbell shaped channel that is locatable between the first and second ends, and a flexible, thin disk that includes a slit. The flexible, thin disk is disposed within the pressure activated two-way slit valve assembly such that the slit resides within the dumbbell shaped channel and is substantially perpendicular to a longitudinal axis of the pressure activated two-way slit valve assembly. The slit and the dumbbell shaped channel of the pressure activated two-way slit valve assembly are sized to enable the slit to deform in response to a predetermined pressure differential across the slit to allow fluid to pass therethrough.

Embodiments of this aspect of the invention can include the following features. In one embodiment, the wall of the pressure activated two-way slit valve assembly further defines connection ports that are located at the first and second ends. These connection ports are in fluid communication with the dumbbell shaped channel. In some embodiments, the first end of the pressure activated two-way slit valve assembly has a barbed ending for attaching to a catheter or other similar medical device. In another embodiment, the second end of the pressure activated two-way slit valve assembly has a luer ending for attaching to one of a dialysis machine or an end cap. In some embodiments, the flexible, thin disk has a straight slit. In other embodiments, the flexible, thin disk has an H-shaped slit. In another embodiment, the slit of the flexible, thin disk has a saw-tooth wave shape. In still yet another embodiment, the pressure activated two-way slit valve assembly includes a safety rotatable valve key that overrides the functionality of the pressure activated two-way slit valve assembly and maintains the pressure activated two-way slit valve assembly in an open position. In a further embodiment, the safety rotatable valve key is attached to the second end of the pressure activated two-way slit valve assembly.

In another aspect, the invention relates to a medical device. The medical device includes a catheter including a distal end, a proximal end, and a housing that defines one or more lumens that extend between the distal end and the proximal end. The distal end of the catheter is open whereas the proximal end is attached to a pressure activated two-way slit valve assembly comprising a first end, a second end, a wall defining a dumbbell shaped channel that is locatable between the first and second ends, and a flexible, thin disk including a slit. The flexible, thin disk is disposed within the pressure activated two-way slit valve assembly such that the slit resides within the dumbbell shaped channel and is substantially perpendicular to a longitudinal axis of the pressure activated two-way slit valve assembly. The slit and the dumbbell shaped channel are sized to enable the slit to deform in response to a predetermined pressure differential across the slit to allow fluid to pass therethrough.

Embodiments of this aspect of the invention can include the following features: In one embodiment, the wall of the pressure activated two-way slit valve assembly further defines connection ports that are located at the first and second ends of the pressure activated two-way slit valve assembly and are in fluid communication with the dumbbell shaped channel. In another embodiment, the flexible, thin disk has an H-shaped slit. Alternatively, in another embodiment, the slit of the flexible, thin disk has a saw-tooth wave shape. In some embodiments, the pressure activated two-way slit valve assembly further includes a safety rotatable valve key that overrides the functionality of the pressure activated two-way slit valve assembly and maintains the pressure activated two-way slit valve assembly in an open position. In a further embodiment, the safety rotatable valve key is attached to the second end of the pressure activated two-way slit. valve assembly. In still yet another embodiment, the housing of the catheter is coated with an anti-infective coating to inhibit cell and bacteria growth.

In general, in another aspect, the invention relates to a valved dialysis catheter. The valved dialysis catheter, according to this aspect of the invention, includes an open-ended single or multi-lumen catheter including at least one lumen for withdrawing blood from a patient for dialysis and at least one lumen for returning blood from a dialysis machine to the patient, Each lumen of the open-ended multi-lumen catheter includes a pressure activated two-way slit valve assembly. Each pressure activated two-way slit valve assembly includes a first end that is connected to the open-ended single or multi-lumen catheter, a second end that is connectable to a dialysis machine, a wall extending between a first end and a second end and defining a dumbbell shaped channel that is locatable between the first and second ends, and a flexible, thin disk. The flexible thin disk includes a slit and is disposed within the pressure activated two-way slit valve assembly such that the slit resides within the dumbbell shaped channel and is substantially perpendicular to a longitudinal axis of the pressure activated two-way slit valve assembly. Both of the slit and the dumbbell shaped channel are sized to enable the slit to deform in response to a predetermined pressure differential across the slit to allow fluid to pass therethrough.

Embodiments of this aspect of the invention can include the following features. In one embodiment, the wall of the pressure activated two-way slit valve assembly further defines connection ports that are located at the first and second ends of the pressure activated two-way slit valve assembly. These connection ports are in fluid communication with the dumbbell shaped channel. In some embodiments, the first end of the pressure activated two-way slit valve assembly has a barbed ending connecting the pressure activated two-way slit valve assembly with the multi-lumen catheter. In other embodiments, the second end of the pressure activated two-way slit valve assembly has a luer ending for attaching to one of a dialysis machine or an end cap. In another embodiment, the flexible, thin disk has an H-shaped slit. Alternatively, in a further embodiment, the slit of the flexible, thin disk has a saw-tooth wave shape. In some embodiments, the pressure activated two-way slit valve assembly includes a safety rotatable valve key that overrides the functionality of the pressure activated two-way slit valve assembly and maintains the pressure activated two-way slit valve assembly in an open position. Other embodiments feature a single or multi-lumen catheter with an anti-infective external surface and further embodiments feature a single or multi-lumen catheter with an anti-infective internal surface.

In general, in another aspect, the invention relates to a method for preventing air ingestion in a valved catheter and preventing blood loss from the valved catheter. The method, according to this aspect of the invention, includes providing the medical device including the catheter described above, and using the pressure activated two-way slit valve assembly to prevent air ingestion through the catheter and into a patient's blood stream and to prevent blood loss while the valved catheter is not in use.

Embodiments of this aspect of the invention can include the following features. In one embodiment, the predetermined pressure differential across the slit of the disk within the pressure activated two-way slit valve is between about 50 cm of water and about 120 cm of water. In an alternative embodiment, the predetermined pressure differential is between about 80 cm of water and 120 cm of water. In other embodiments, the valve is designed to open at any predetermined pressure selected by a manufacturer.

The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

FIG. 1 is schematic view of one embodiment of a pressure activated two-way slit valve assembly according to the invention.

FIG. 2 is an exploded view of the pressure activated two-way slit valve assembly of FIG. 1.

FIG. 3 is a cross-sectional view of a first end portion of the pressure activated two-way slit valve assembly, taken along line AA of FIG. 1.

FIG. 4 is a cross-sectional view of a second end portion of the pressure activated two-way slit valve, assembly, taken along line BB of FIG. 1.

FIG. 5 is a plan-view of an alternative embodiment of a lumen extending through the first and second end portions.

FIG. 6 is another plan-view of another alternative embodiment of a lumen extending through the first and second end portions.

FIG. 7 is a plan-view of a flexible, thin disk that is disposed within the pressure activated two-way slit valve assembly of FIG. 1.

FIG. 8 is a plan-view of another embodiment of a flexible, thin disk.

FIG. 9 is a schematic view of one embodiment of a medical device that includes a catheter and two pressure activated two-way slit valve assemblies.

FIG. 10 is a cross-sectional view of a portion of the catheter, taken along line CC of FIG. 9.

FIG. 11 is a cross-sectional view of a portion of a tubular element extending off from the catheter, taken along DD of FIG. 9.

FIG. 12 is a schematic view of an embodiment of a safety, rotatable valve key.

FIG. 13 is a schematic view of the safety, rotatable valve key of FIG. 12 attached to a second end of the pressure activated two-way slit valve assembly of FIG. 1.

FIG. 14 is a schematic view of a valved dialysis catheter including two pressure activated two-way slit valve assemblies as used during hemodialysis.

DESCRIPTION

The kidneys are a pair of organs located near the backbone that filter and remove waste products from a human being's blood. Patients who suffer from kidney failure must undergo hemodialysis, a process in which waste products from the patient's blood are removed through passing their blood through a dialysis machine. Generally, these patients require dialysis treatments once every three days.

Hemodialysis catheters, which are a type of high flow rate catheter, are used to transport such a patient's blood to and from the dialysis machine for treatment. Typically, a portion of the hemodialysis catheter is implanted within a patient's body while a reminder of the hemodialysis catheter extends out from the body and is easily attached to the dialysis machine.

Other uses for high flow rate catheters can include rapid infusion of blood and blood products to a patient and infusion of saline to a dehydrated patient.

Some of the biggest complaints with conventional high flow rate catheters are occlusions, thrombus, and catheter-related infections. Generally, these complications arise due to, at least in part, poor fluid flow dynamics of the catheter and/or catheter parts, including, but not limited to, valve assemblies.

The present invention concerns valve assemblies for high flow rate catheters having a single lumen or multiple lumens. A valve assembly, according to the present invention, in combination with a catheter allows for efficient fluid transport to and/or from a patient's body. This invention also concerns a valve assembly for a high flow rate catheter that prevents ingestion of air from entering the high flow rate catheter and prevents blood loss when the catheter is not in use.

Referring to FIG. 1, a pressure activated two-way slit valve assembly 10 according to the invention includes a first end 12, a second end 14, and a wall 15 extending from the first end 12 to the second end 14. The wall 15 can be made from any relatively rigid, biocompatible, polymer such as, for example, polycarbonate, polyethylene, or Ultem® and includes a female housing portion 16 and a male housing portion 18. The male housing portion 18 friction fits within the female housing portion 16, thereby holding the two portions 16, 18 together. In addition to frictional forces, an adhesive can be used to secure a bond between the female and male housing portions 16, 18. Alternatively, the female housing portion 16 can be thermally, chemically, or ionically bonded to the male housing portion 18.

Located at the first and second ends 12, 14 are connection ports 17 and 19 used to interconnect the pressure activated two-way slit valve assembly 10 to other medical devices, such as, for example, catheters, dialysis machines, and end caps. The connection ports 17, 19 can have barbed or luer endings as shown in FIGS. 1 and 2 to aid in attachment between a medical device and the pressure activated two-way slit valve assembly 10. For example, the connection port 17 has barbed endings 47 and the connection port 19 has luer endings 48.

Disposed within the pressure activated two-way slit valve assembly 10 is a flexible, thin disk 24, shown in FIG. 2, that is “sandwiched” between the female housing portion 16 and the male housing portion 18. The flexible; thin disk 24 is preferably made from silicone or other similar flexible polymer and includes a slit 26. The flexible, thin disk 24 is positioned within the pressure activated two-way slit valve assembly 10 such that the slit 26 is perpendicular to line LL, a longitudinal axis 25 of the pressure activated two-way slit valve assembly 10. The slit 26 remains in a closed position as shown in FIG. 2 until a pressure differential having a predetermined force exists within the pressure activated two-way slit valve assembly 10. Once the pressure differential crosses over this predetermined force threshold, the slit 26 separates, thereby allowing blood or fluid to flow therethrough.

The pressure activated two-way slit valve assembly 10 also includes a dumbbell shaped channel 20 that is defined by wall 15 and surrounds the flexible, thin disk 24. As shown in FIGS. 3 and 4, the dumbbell shaped channel 20 is disposed within both of the female housing portion 16 and the male housing portion 18. The dumbbell shaped channel 20 has a middle channel portion 27 disposed between and in fluid communication with two large cross-sectional area channel portions 28. The middle portion 27 has a smaller cross-sectional area than the two large cross-sectional area channel portions 28 and thus, restricts the slit 26 from opening prematurely (i.e., under conditions where the pressure differential is below threshold) by decreasing the amount of channel cross-sectional area in a pressure sensitive region. In some embodiments, each large cross-sectional area channel portion 28 has 3 times the cross-sectional area as the middle portion 27. This extra cross-sectional area of the large cross-sectional area channel portions 28 provides the pressure activated two-way slit valve assembly 10 with a large amount of fluid transport area, to maximize fluid flow rates through the pressure activated two-way slit valve assembly 10 once the slit 26 has cracked open. These large cross-sectional area channel portions 28 allow the flow rate through the pressure activated two-way slit valve assembly 10 to maintain a flow rate of up to 500 ml/min. In some embodiments, the large cross-sectional area channel portions 28 allow the flow rate to approach a flow range of about 400 ml/min to 500 ml/min, which is a greater flow rate range than typically achieved in conventional valved high flow rate catheters. An advantage of this greater flow rate range is a decrease in actual catheter use or treatment time. For example, a hemodialysis catheter having a greater flow rate range means that there will be a decrease in dialysis treatment time, which is a greater convenience for both a dialysis patient and for an attending medical professional.

The shape of the dumbbell shaped channel 20 can be slightly modified to produce alternative embodiments of the pressure activated two-way slit valve assembly 10. As depicted in FIGS. 5 and 6, the perimeter of the large cross-sectional area channel portion 28 can be extended to form an elongated dumbbell shaped channel 20 b, shown in FIG. 5, or an octagonal dumbbell shaped channel 20 c, as shown in FIG. 6. In some embodiments, the size of the middle channel portion 27 is minimized such that the two large cross-sectional area channel portions 28 are separated by a millimeter or less. Other similar embodiments are also possible as long as each large cross-sectional area channel portion 28 has a larger cross-sectional area than the middle portion 27.

Each of the female and male housing portions 16, 18 can taper, as depicted in FIG. 1, from an area of greatest diameter located substantially at connection area 23 to an area of lesser diameter 21. The dumbbell shaped channel 20 disposed within the female and male housing portions 16, 18 tapers along with these portions 16, 18. As the dumbbell shaped channel 20 tapers the shape of the dumbbell shaped channel 20 gradually transforms from a dumbbell structure to an oval or circular structure.

Located within the dumbbell shaped channel 20, between the female housing portion 16 and the male housing portion 18, is the flexible, thin disk 24 with slit 26. The slit 26 can be a straight slit or, in some embodiments, be H-shaped as shown in FIG. 7. Alternatively, the slit 26 can have a saw-tooth wave shape as shown in FIG. 8. In any case, the size and shape of the slit 26 and the size of the dumbbell shaped channel 20 are designed to enable the slit to deform or crack open when a predetermined pressure differential exists across the pressure activated two-way slit valve assembly 10. Generally, the size of the slit 26 and the dumbbell shaped channel 20 are designed to prevent deformation of the slit 26 until a pressure differential of at least about 50 cm of water exists, thereby minimizing accidental openings of slit 26, which could lead to bleed out or air ingestion. In a preferred embodiment, the dumbbell shaped channel 20 is designed to prevent deformation of the slit 26 until a pressure differential within a range of about 50 cm of water to about 120 cm of water exists. In a more preferred embodiment, the dumbbell shaped channel is designed to prevent deformation of the slit until a pressure differential within a range of about 80 cm of water to about 120 cm of water exists. It is also important to note that the valve may be designed to have the slit crack open at any pressure differential preferred for a particular medical application.

The two-way slit valve assembly 10 allows fluid to flow therethrough in either a proximal direction (i.e., from the first end 12 towards the second end 14) or a distal direction (i.e., from the second end 14 towards the first end 12). As long as the pressure differential across the flexible, thin disk 24 is greater than the threshold, the slit 26 will open automatically and will allow fluids to pass therethrough in either direction.

The particular threshold pressure differential is determined by one or more of the following factors: (1) the thickness of the flexible, thin disk 24, (2) the size of the slit 26, (3) the hardness of the material used to form the flexible, thin disk 24, and (4) the cross-sectional area of the dumbbell shaped channel 20 within each of the female housing portion 16 and the male housing portion 18. For example, the threshold pressure differential value of the two-way slit valve assembly 10 can be customized to a particular value by varying the factors listed above. Thus, if a particular application of the two-way slit valve assembly 10 required a valve, which could open a very low threshold pressure differential value, the material and thickness of the flexible, thin disk 24 and the length of the slit 26 can be selected to accomplish this usage.

In some applications of the two-way slit valve assembly 10, it is important to provide the valve with two different threshold pressure differential values. That is one particular threshold pressure differential value for fluids flowing in the proximal direction and another different threshold pressure differential value for fluids flowing in the distal direction. Embodiments of two-way slit valve assemblies 10 used in these applications can include a dumbbell shaped channel 20 that has a different cross-sectional area dimension in the female housing portion 16 than in the male housing portion 18, so as create two direction sensitive threshold pressure differential values.

The two-way slit valve assembly 10 can be attached to a catheter having a single lumen or alternatively multiple lumens. By way of illustration the following example describes usage of the two-way slit valve assembly in connection with a hemodialysis catheter (a high flow rate catheter) that has two or more lumens.

Referring to FIG. 9, shown is a portion of a hemodialysis catheter 40 attached to two pressure activated two-way slit valve assemblies 10 a, 10 b according to the invention. The hemodialysis catheter 40 has two distinct lumens 42 a, 42 b disposed within, as shown in FIG. 10. One of the lumens 42 a provides a path for waste-filled blood to exit the patient's body, while the opposing lumen 42 b provides a path for blood after dialysis treatment to return to the body. An adapter 34, shown in FIG. 9 and affixed to an end of the hemodialysis catheter 40 further separates these two distinct lumens 42 a, 42 b into individual tubular elements generally called extension legs 30.

Each extension leg 30 has a single lumen 32 disposed within as shown in FIG. 11. The pair of extension legs 30 a, 30 b work in combination. One of the extension legs 30 a is in fluid connection with the lumen 42 a that transports waste-filled blood to a dialysis machine, while the other extension leg 30 b is connected to the lumen 42 b that carries treated, clean blood back to the patient. Each extension leg 30 a, 30 b is connected to a pressure activated two-way slit valve assembly 10 that prevents blood from flowing therethrough when dialysis is not in process. The hemodialysis catheter 40 in combination with the extension legs 30 a, 30 b and pressure-activated slit valve assemblies 10 a, 10 b can be secured to a patient's body using a wing clip 36 as shown in FIG. 9.

The embodiments shown in FIGS. 9 and 10 depict a hemodialysis catheter 40• having two lumens 42 a, 42 b. In alternative embodiments, not shown, the hemodialysis catheter 40 or other high flow rate catheter can have more than two lumens. In these embodiments, the additional lumens (i.e., the third, fourth, and so on) can provide access ports for delivery of liquid medicines or other fluids to the patient or for collecting blood specimens from the patient's body. Additional extension legs 30 to connect to the additional lumens 42 would be needed. Each additional extension leg 30 can be outfitted with one pressure activated two-way slit valve assembly 10 if desired.

In some embodiments of this invention, an outer surface 45 of the hemodialysis catheter 40 is coated with an anti-infective coating, such as an antibiotic (for example, tetracycline or doxycycline) or an antimicrobial. These anti-infective coating help prevent the build up of bacteria on the surface of the hemodialysis catheter 40, thereby helping to minimize the possibility of complications caused by infection. The hemodialysis catheter can also have a similar anti-infective coating along a surface 47 of the lumen 42 a, 42 b. Likewise, the anti-infective coating present along the surface 47 helps to prevent infection within the hemodialysis catheter 40.

An additional feature that can be incorporated into the invention is a safety rotatable valve key 50, an embodiment of which is shown in FIGS. 12 and 13. The safety rotatable valve key 50 can be used force and maintain the slit 26 open to allow for immediate and constant access to the lumens 42 of the hemodialysis catheter 40. The safety rotatable valve key 50 includes an inner tube 52 that can be positioned to extend through the slit 26 when the safety rotatable valve key 50 is rotated from a first position to a second position. The safety rotatable valve key 50 can include a luer ending 54 for attachment to a dialysis machine or an end cap. In addition, the safety rotatable valve key 50 can also include a pair of finger knobs 56 a, 56 b to aid a medical professional in rotating the safety rotatable valve key 50.

In operation, a portion of the hemodialysis catheter 40 is implanted within the patient's body and an open end of the hemodialysis catheter 40 is located within the patient's blood stream. To begin hemodialysis, endcaps are removed from the second end 14 of each pressure activated two-way slit valve assembly 10 a, 10 b attached to the hemodialysis catheter 40. The second end 14 is then secured to a dialysis machine 60, shown in FIG. 14, that supplies sufficient vacuum force to create the required pressure differential across one the slit 26 of one of the pressure activated two-way slit valve assemblies 10 a. Once the slit 26 has cracked open, blood will flow from the patient's body through the hemodialysis catheter 40 to the dialysis machine 60 for treatment (i.e., removal of waste products from the blood). Simultaneously, the dialysis machine 60 forces treated blood through another pressure activated two-way slit valve assembly 10 b and into the hemodialysis catheter to be returned to the patient's body.

Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and scope of the invention. The invention is not to be limited only to the preceding illustrative description. 

What is claimed is:
 1. A pressure activated slit valve assembly for a catheter, comprising: a housing defining a lumen therethrough, the lumen having a longitudinal axis; and a membrane disposed across the lumen, said membrane having a slit therethrough, wherein the lumen has a substantially dumbbell shaped cross-section, the cross-section lying in a plane perpendicular to the longitudinal axis.
 2. The pressure activated slit valve assembly of claim 1, wherein the slit deforms to permit fluid flow when exposed to a fluid pressure differential of at least a predetermined threshold, and wherein the dumbbell shaped lumen and the slit are sized to prevent deformation of the slit until a fluid pressure of between 50 cm of water and 120 cm of water exists.
 3. The pressure activated slit valve assembly of claim 1, wherein the dumbbell shaped cross-section is defined by two flanking regions connected by a central region, Wherein the cross-sectional area of the central region is less than that of the flanking regions.
 4. The pressure activated slit valve assembly of claim 3, wherein each of said flanking regions has a cross-sectional area roughly equal to three times that of the central region.
 5. The pressure activated slit valve assembly of claim 3, wherein the cross-sectional areas of said flanking regions and said central region are chosen to admit flows of up to 500 ml/min.
 6. The pressure activated slit valve assembly of claim 1, wherein the cross-sectional area of the lumen on opposite sides of the membrane varies along a taper from a relative maximum nearest the membrane to a relative minimum farthest from the membrane.
 7. The pressure activated slit valve assembly of claim 1, wherein each of the housing and the membrane have a substantially elliptical outer cross-section.
 8. A pressure activated slit valve assembly for a catheter, comprising: mateable male and female housing portions defining a recess at their junction, each housing portion having an oblong lumen, the lumen having a longitudinal axis; and a flexible membrane sandwiched between said mateable housing portions within said recess, the membrane having a slit therethrough, wherein each oblong lumen has a cross-section with a relatively narrow central portion connecting two relatively large end portions, the cross-section lying in a plane perpendicular to the longitudinal axis.
 9. The pressure activated slit valve assembly of claim 8, wherein said end portions each have a cross-sectional area roughly equal to three times that of the central portion.
 10. The pressure activated slit valve assembly of claim 8, wherein the oblong lumen and the saw-toothed slit are sized to admit flows of up to 500 ml/min.
 11. The pressure activated slit valve assembly of claim 8, wherein the saw-toothed slit deforms to permit fluid flow when exposed to a fluid pressure differential of at least a predetermined threshold, and wherein the oblong lumen and the saw-toothed slit are sized to prevent deformation of the slit until a fluid pressure of between 50 em of water and 120 em of water exists.
 12. The pressure activated slit valve assembly of claim 8, wherein the cross-sectional area of the lumen in each of the male and female housing portions varies along a taper from a relative maximum nearest the membrane to a relative minimum farthest from the membrane.
 13. The pressure activated slit valve assembly of claim 8, wherein the housing and the membrane have a substantially elliptical outer cross-section.
 14. A medical device, comprising: a catheter having a distal end insertable into a body lumen of a patient, a proximal end opposite the distal end, and at least one lumen extending therethrough; and at least one valve assembly, each valve assembly comprising: a housing having a first end connectable to the proximal end of the catheter and a second end opposite the first end, the housing defining a valve lumen capable of fluid communication with a lumen of the catheter, the valve lumen having a longitudinal axis, said valve lumen having an oblong cross-section defined by two flanking regions connected by a central region, the cross-section lying in a plane perpendicular to the longitudinal axis, wherein the cross-sectional area of the central region is less than that of the flanking regions; and a membrane having a slit therethrough, said slit being oriented about an axis substantially parallel to the length of the valve lumen.
 15. The medical device of claim 14, wherein each of said flanking regions has a cross-sectional area roughly equal to three times that of the central region.
 16. The medical device of claim 14, wherein the oblong lumen and the slit are sized to admit flows of up to 500 ml/min.
 17. The medical device of claim 14, wherein the saw-toothed slit deforms to permit fluid flow when exposed to a fluid pressure differential of at least a predetermined threshold, and wherein the lumen and the saw-toothed slit are sized to prevent deformation of the slit until a fluid pressure of between 50 cm of water and 120 cm of water exists.
 18. The medical device of claim 14, wherein the cross-sectional area of the lumen on opposite sides of the membrane varies along a taper from a relative maximum nearest the membrane to a relative minimum farthest from the membrane.
 19. The medical device of claim 14, wherein the housing and the membrane have a substantially elliptical outer cross-section. 